This application relates to wireless communication systems and techniques for wireless communications using one or more relay stations in addition to base stations.
Wireless communication systems use electromagnetic waves to communicate with fixed and mobile wireless communication devices, e.g., mobile wireless phones and laptop computers with wireless communication cards, that are located within cells of coverage areas of the systems. A radio spectral range or band designated or allocated for a wireless communication service or a particular class of wireless services may be divided into different radio carrier frequencies for generating different communication frequency channels. Such systems use base stations spatially distributed to provide radio coverage in a geographic service area which is divided into cells. In such a cellular deployment, each base station (BS) is conceptually located at the center of a respective cell to provide radio coverage for that cell and transmits information to a wireless subscriber station (SS) such as a mobile SS (MSS) via BS-generated downlink (DL) radio signals. A subscriber station at a particular cell transmits information to its serving base station for that particular cell via uplink (UL) radio signals. The base stations can include directional antennas to further divide each cell into different cell sectors where each antenna covers one sector. This sectorization of a cell increases the communication capacity.
The radio coverage of a network of fixed base stations may be limited due to various factors. Various structures may block the radio signals of certain base stations. For example, a tall building may shield a particular area from the radio signal from a base station, thus creating an undesired shadowing. At the edge of a radio cell, the signal strength can be weak and hence can increase the error rate in the wireless communications. One approach to mitigating these and other limitations is to increase the number of base stations in a given service area. In one implementation under this approach, one or more relay stations (RSs) can be deployed among certain fixed base stations to relay communication signals between a subscriber station and a base station, thus extending the coverage and improving the communication capacity and quality of the base station. A relay station may be a fixed transceiver or a mobile transceiver station depending on the specific conditions for deploying such as relay station. A subscriber station (SS) signal may hop through one or more RSs before reaching a serving base station. The proposed IEEE 802.16j provides Multi-hop Relay (MR) modes to use relay stations for enhanced coverage and service to subscribers. A multi-hop relay wireless network under IEEE 802.16j can include MR base stations (MR-BSs) with the support of the Multi-hop Relay modes. A relay station can be fixed, nomadic or mobile. A wireless relay access network supports data transmission between BS and MS either directly or through one or more RSs. IEEE 802.16j defines air interface standard for a wireless relay access network based on OFDMA technology.